Feasibility Study of InfraredDetection of Defects in Green-State

and Sintered PM Compacts

Souheil Benzerrouk

Worcester Polytechnic InstituteNovember 15th, 2006

Particulate Material Research Center

Reinhold Ludwig

2

Objectives

Development of a thermo-electric testingapparatus capable of detecting surface and sub-surface flaws in green-state compacts with twooptions:

On-line, relying on natural convection for surface andmajor subsurface defects (passive)

Off-line using a pulsed thermography scheme throughinduction heating for small subsurface flaws and forelaborate analysis (active)

3

Summary of accomplishments Developed a complete theoretical formulation and several models

were devised:

DC step heating

Inductive heating

Defect Parameters

Established a comprehensive finite elements model which includes:

3-D DC heating

Axis-symmetric transient

3D inductive heating

4

Summary of accomplishments Constructed a test system capable of:

Inducing current through the part (DC & AC)

Acquiring thermal data

Real time defect detection

Designed a factory friendly software with the following features:

Camera control and operation

Real time data collection and processing

Friendly user interface

5

Summary of accomplishments Conducted extensive testing in:

Lab setting with a DC and an AC current source

Manufacturing setting:

Simple compacts

Complex gear made at high rate

Defective parts

Aluminum components

6

IR Imaging Technology requires heat source Special camera to record thermal signature Elaborate signal acquisition and processing steps to form

image Additional image analysis post-processing

SUT

Heat source

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IR Imaging- Pros and Cons

Pros: Remote sensing capability Fast response High spatial resolution High temperature range Cameras have built-in image processing capability

Cons: Need for straight viewing corridor with the target Background calibration Cost is primarily determined by camera

8

Simple Subsurface Defect Model

Sig n a tu re d u e to

a su b su rfa ce fla w

T im e

T e m p e ra tu re

!

2z

t "

3

1

zc !

These defects will appearwith a reduced contrast

t observation time, z depthof the defect , α thermaldiffusivity, c loss of contrast

Subsurface defects willappear at a later time

PM Pa rt

D e fe cts

Su rfa ce T e m p e ra tu re

9

FEM Formulation

Static modeling in 2D - Sensitivity study Surface and Subsurface defects Combination of flaws (various sizes and orientations)

Dynamic modeling in 2D - sensitivity study Extend the 2D model to include the dynamic effects

Dynamic modeling in 2D – Induction heating Electromagnetic model with heat transfer

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FEM Formulation (Combined Static)

1mm x 1mmDefect

20µm x 100µmDefects

Defects’ signature

11

Transient Model

Currentstep

t =0.2 sec

t =1 sec

12

Transient Modelt =10 sec

13

FEM Modeling (Induction)

Modeling

Space

P/M SampleDefect

Induction coil

Model parameters: Green state cylinder

with: 7.25 g/cm3 r=1.5 cm, z=6 cm

Copper inductioncoil with watercooling

14

Experimental Testing

Static imaging Green state parts Surface flows, with various shapes,

sizes and orientations Apply simple thresholding algorithm

Dynamic imaging Simple green state and sintered

parts Complex gears

15

Test Arrangement

DC Power supply

Motorized presssystem

An IR camera at0.3m away from thesample under test

A computer forprocessing andcamera controls

Contacts

Sample

under test

IR camera

Firewire

Signal processing computer

DC power supply

GPIB

Switch

Function

generator

16

Test Arrangement

A switching circuit,for pulse shapingand synchronousoperation

Presssystem

Painted P/Mpart

IR camera

Switchingcircuit

Controlcomputer

DCPowersupply

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Static Measurements

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Test Arrangement

RS 232

c onne c tion

Timing a nd

sync hroniz a tion unit

Pow e r ge ne ra tor

Compute r Syste m

D a ta stora ge unit

Exte rna l ha rd drive

PM pa rt

Induc tion c oil

IR ima ging Softw a re

Fire w ire

c onne c tion

U SB c onne c tion

RS 232

c onne c tion

RS 232

c onne c tion

IR Ca me ra

19

Test Arrangement (Induction Heating)

A switching circuit for pulse shaping and synchronous operation

FunctionGenerator

InductionCoil

P/M part

IR cameraInductionHeating Supply

Control and DataProcessingComputer

20

Experimental Results: Induction Heating

Part parameters: Green state part

with: 1.0% Cu 0.2% C 0.8% wax

Density range:6.8g/cm3 to7.1g/cm3

Experimental Results

System Settings: F = 50KHz ton= 5sec Ptotal=2kW

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1 cm

Active Testing

Temperature recording when the part is subjected to stepinductive heating of a good part and a defective part

Crack

1 cm

0 10 20 30 40 50 6060

80

100

120

140

160

180

200

220

240

260

Distance along profile

Pixel intensity

0 10 20 30 40 50 60160

170

180

190

200

210

220

230

240

250

260

Distance along profile

Pixel intensity

Crack signature

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On-Line Testing

Parts courtesy of Nichols Portland

Experimental Results

Manufacturing rate perpress: 900parts/hour

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On-Line Testing: Processing

Experimental Results

0 20 40 60 80 100 120 140 160 180120

140

160

180

200

220

240

260

Distance along profile

Pixel Intensity

Setup courtesy of Nichols PortlandProfile along the dotted line

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On-Line Testing: Processing

Experimental Results

Monitoring the temperature of a spot in the production line

308

309

310

311

312

313

314

315

316

317

318

40 42 44 46 48 50

Time (sec)

Te

mp

era

ture

(K

)

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On-Line Testing: Processing

Experimental Results

First derivative in the spatial domain

-4000000

-3000000

-2000000

-1000000

0

1000000

2000000

3000000

4000000

0 20 40 60 80 100 120 140 160 180 200

Series1

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On-Line Testing: Processing

Experimental Results

Second derivative in the spatial domain

-4E+12

-3E+12

-2E+12

-1E+12

0

1E+12

2E+12

3E+12

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Series1

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On-Line Passive TestingSetup courtesy of Metal Powder Products

Camera is setup at 50cm from the press system

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Complete Interactive System

Camera control console

Loading options for the reference frame

Temperature display options

Alarm setup

Display camera info

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Automatic Defect Detection Algorithm

Algorithm implemented in software

50 100 150 200 250 300

50

100

150

200

Center of the defect

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Summary

Completed a thermo-electric inspection system Allows on-line and off-line green-state P/M part testing

with high resolution and speed Features our own calibration and synchronization

methodology Developed an extensive software interface for data

processing and evaluation Have applied for patent protection

Are in the process of commercializing the system Registered a business (S. Benzerrouk, CEO)